2-Alkyl-3-methylfurans have a peculiar fragrance, and many of them are useful in the fragrance-producing industry. For example, rosefuran of the following formula: ##STR2## has a citrus-like fragrance and is known as an important minor component that forms a green top note of rose oil, and it is desired to establish an industrial method for producing it.
For synthetically producing rosefuran via 3,7-dimethyl-2,6-octadien-4-olide, there are known a method starting from 4-methyl-(5H)-furan-2-one and comprising introducing an alkyl side chain into the starting compound to give 3,7-dimethyl-2,6-octadien-4-olide (see D. R. Gedge, G. Pattenden; Tetrahedron Letters, 1977, 4443-4446) (hereinafter referred to as the first method),-and a method starting from methallyl alcohol and comprising seven steps of processing the starting compound for epoxidation, cyanation, etc. to give 3,7-dimethyl-2,6-octadien-4-olide (see S. Takano, M. Morimoto, S. Satoh, K. Ogasawara; Chemistry Letters, 1984, 1261-1262) (hereinafter referred to as the second method).
However, these methods are unsuitable in industrial use in that the first method produces structural isomers as side products while the separation and purification of the intended product from the isomers is difficult and that the second method must use tertiary-butyl peroxide, of which, however, the use of a large amount is dangerous, and requires many steps.